Songs that have Verse order trigger traceback

[Azaziah]

If song has a verse order, traceback is triggered if you try to review or send the song to Live.

Traceback (most recent call last):
  File "E:\bzr\openlp\trunk\openlp\core\lib\mediamanageritem.py", line 477, in on_selection_change
    self.on_preview_click(True)
  File "E:\bzr\openlp\trunk\openlp\core\lib\mediamanageritem.py", line 491, in on_preview_click
    service_item = self.build_service_item()
  File "E:\bzr\openlp\trunk\openlp\core\lib\mediamanageritem.py", line 626, in build_service_item
    if self.generate_slide_data(service_item, item, xml_version, remote, context):
  File "E:\bzr\openlp\trunk\openlp\plugins\songs\lib\mediaitem.py", line 606, in generate_slide_data
    verse_def = '{tag}{label}'.format(tzg=verse_tag, text=verse[0]['label'])
KeyError: 'tag'

Trunk rev 2674.